Maybe I'm the only one who's concerned about this, but to drive five pairs of speakers, even with the Adcom switcher, you would need an amp that is stable to very low impedance swings. The only amps I know that can do that and aren't too expensive are second hand Aleph series Pass Labs amps. These can be had for around $600-800. Here's an Aleph 3 that's currently at $416 on eBay:

http://cgi.ebay.com/ws/eBayISAPI.dll...MEWA%3AIT&rd=1

Keep in mind that these amps run rather warm and they won't be cranking out lots of amps, but that's OK for your application, I think. Harman amps are also quite stable, but the newer ones may not be as good as the ones from a decade or so ago.